Waterborne polyurethane with good water resistance and preparation method thereof

Abstract

The invention discloses waterborne polyurethane with good water resistance and a preparation method thereof, and the preparation method comprises the following preparation steps: (1) carrying out vacuum dehydration on polyol, an anionic hydrophilic chain extender and a nonionic hydrophilic chain extender containing a polyoxyethylene side chain, adding polyisocyanate, and carrying out polymerization reaction to prepare a polyurethane prepolymer; (2) dispersing the polyurethane prepolymer into water under high-speed stirring to obtain a prepolymer emulsion; and (3) dropwise adding a mixed solution of a water-insoluble diamine post-chain extender containing hydrophobic chain links and an organic solvent into the prepolymer emulsion, and stirring for reaction to obtain the waterborne polyurethane with good water resistance. The prepared waterborne polyurethane has the advantages of being excellent in stability, small in particle size and good in water resistance.

Description

Technical Field

[0001] The invention relates to the technical field of waterborne polyurethane, in particular to a waterborne polyurethane nanoemulsion with good water resistance and a preparation method thereof. Background Art

[0002] Waterborne polyurethane uses water as a dispersion medium, contains no or a small amount of VOC, and is non-toxic, safe, reliable, environmentally friendly, and has excellent comprehensive performance. Waterborne polyurethane molecules have a block structure with alternating soft segments and hard segments, and have good "tailorability". By optimizing the composition and structure of waterborne polyurethane, it can have excellent mechanical properties, high adhesion, good heat resistance, etc. Therefore, waterborne polyurethane is widely used in waterborne coatings, digital inkjet inks, adhesives, leather finishing agents and other fields.

[0003] In the process of waterborne polyurethane synthesis, hydrophilic groups need to be introduced to disperse it in water to form a stable emulsion. The content of hydrophilic groups is the most direct and key factor affecting the particle size of waterborne polyurethane emulsion. The larger the content of hydrophilic groups, the smaller the particle size of the emulsion. Generally speaking, waterborne polyurethane emulsions with small particle size, especially those with nanometer size, have the characteristics of stable storage, easy film formation and excellent film performance. Especially when waterborne polyurethane emulsions are used for water-based digital inkjet printing inks, waterborne polyurethane emulsions with nanometer particle size can greatly reduce the risk of inkjet printer nozzle clogging and ensure the continuity and stability of the printing process, which is crucial to the quality of inkjet printing products and their continuous industrial production process. However, generally speaking, the smaller the particle size of the waterborne polyurethane emulsion, the more hydrophilic groups in its molecular structure, the worse the water resistance of the obtained product, which may eventually cause the waterborne polyurethane to lose its application value. Therefore, it is very necessary to prepare a waterborne polyurethane with small particle size and good water resistance.

[0004] Introducing hydrophobic chain link in the molecular structure of waterborne polyurethane, improving the content of hydrophobic chain link, is a kind of effective method that improves the water resistance of waterborne polyurethane.According to the synthesis process of waterborne polyurethane, hydrophobic group can be introduced before polyurethane prepolymer emulsification dispersion forms emulsion or after emulsification dispersion forms emulsion.For the former, can synthesize the polyurethane prepolymer with strong hydrophobicity by preferably containing the polyol of hydrophobic chain link, small molecule diol or hydrophobic isocyanate etc., but this kind of strong hydrophobic polymer is difficult to form stable, waterborne polyurethane emulsion with nanoparticle diameter when adding water emulsification.For the latter, can first polyurethane prepolymer emulsification obtains waterborne polyurethane prepolymer emulsion with nanoparticle diameter in water, and then introduce hydrophobic chain link by post chain extension reaction (generally using diamine post chain extender), thereby make the waterborne polyurethane emulsion containing hydrophobic chain link when emulsion particle diameter is basically unchanged or changes very little. Studies have shown that for water-soluble hydrophobic diamine post-chain extenders, this is an effective method for preparing aqueous polyurethane emulsions with both hydrophobicity and nanoparticle size. However, in order to obtain stronger hydrophobicity, water-insoluble diamine post-chain extenders can be used. However, water-insoluble diamine post-chain extenders (generally diamine compounds containing long carbon chains, polyaromatic rings or polyalicyclic rings) are difficult to be evenly dispersed in the emulsion system formed by common polyurethane prepolymers. Therefore, the post-chain extension reaction of such water-insoluble diamines is not uniform, which will cause the particle size of the aqueous polyurethane emulsion after chain extension to become larger and the stability to become worse. At present, there is not much research on such water-insoluble diamine post-chain extenders. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing waterborne polyurethane. The waterborne polyurethane provided by the present invention has small particle size, excellent stability and good water resistance.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing waterborne polyurethane with good water resistance comprises the following preparation steps:

[0008] (1) vacuum dehydrating a polyol, an anionic hydrophilic chain extender, and a nonionic hydrophilic chain extender containing a polyoxyethylene side chain, and then adding a polyisocyanate to carry out a polymerization reaction to obtain a polyurethane prepolymer;

[0009] (2) dispersing the polyurethane prepolymer into water under high-speed shearing conditions, emulsifying and shearing, to obtain a prepolymer emulsion;

[0010] (3) adding a mixed solution of a water-insoluble diamine post-chain extender containing hydrophobic chain segments and an organic solvent to the prepolymer emulsion obtained in step (2), stirring and reacting, and obtaining a water-based polyurethane with good water resistance.

[0011] Preferably, the water-insoluble diamine post-chain extender containing hydrophobic chain segments in step (3) comprises a mixture of one or more of 3,5-diethyltoluenediamine, 4,4-diaminodicyclohexylmethane, 4,4-diaminodiphenylmethane, N,N-di-sec-pentylcyclohexanediamine, 2,4,4-trimethylhexamethylenediamine, 2-aminobenzamide toluenediamine, and 3,5-dimethylthiotoluenediamine. More preferably, 4,4′-diaminodicyclohexylmethane having a symmetrical structure and strong hydrophobicity is used as the post-chain extender.

[0012] Preferably, the anionic hydrophilic chain extender in step (1) includes a carboxylic acid chain extender and a sulfonate chain extender, more preferably dimethylol propionic acid (DMPA); the nonionic hydrophilic chain extender is a diol containing a polyoxyethylene side chain, trimethylolpropane polyethylene glycol monomethyl ether, and commercial products include Ymer TM N120, Evonik Tegomer D 3403, etc.; the polyols are polyether polyols and polycarbonate polyols with a molecular weight of 1000-2000.

[0013] Preferably, the polyether polyol is a mixture of one or more of polytetramethylene glycol (PTMG) and polyoxypropylene glycol (PPG); the polycarbonate polyol is a mixture of one or more of aliphatic polycarbonate polyol and aromatic polycarbonate polyol; among which aliphatic polycarbonate polyol is more preferred, including PH200 of UBE Company, PHC of Kuraray Company, etc., and the obtained waterborne polyurethane has excellent water resistance.

[0014] Preferably, the polyisocyanate is hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H 12 Isophorone diisocyanate (IPDI) is more preferred, and the resulting aqueous polyurethane emulsion has excellent yellowing resistance, water resistance, heat resistance and other properties.

[0015] Preferably, the polyol, polyisocyanate, anionic hydrophilic chain extender, nonionic hydrophilic chain extender and post-chain extender added in step (1) account for 50% to 60%, 25% to 32%, 2.5% to 5%, 2.5% to 5% and 2% to 4% of the solid matter of the obtained waterborne polyurethane, respectively.

[0016] Preferably, the vacuum dehydration conditions in step (1) are to raise the temperature to 110-120° C., control the vacuum degree in the reactor to 0.08 MPa-1 MPa after the raw materials are melted, and dehydrate for 1-2 hours.

[0017] Preferably, a catalyst is added to the polymerization reaction in step (1), and the reaction is carried out at a temperature of 75 to 85° C. for 2 to 3 hours, and then a mixture of an alcohol small molecule chain extender and an organic solvent is added dropwise, and the reaction is continued for 1 to 2 hours; finally, the temperature is lowered to 35 to 50° C., an organic solvent is added to reduce the viscosity of the prepolymer, and then a neutralizer is added to react for 0.5±0.1 hours to obtain a polyurethane prepolymer.

[0018] Preferably, the alcohol small molecule chain extender is at least one of ethylene glycol, 1,4-butanediol, hexanediol, and diethylene glycol; the catalyst is at least one of dibutyltin dilaurate and stannous octoate; 1,4-butanediol is more preferred. After the small molecule chain extender with a symmetrical structure reacts with isocyanate, it can effectively increase the hard segment content in the chain segment and promote crystallization, and the obtained water-based polyurethane has good hardness and water resistance.

[0019] Preferably, the neutralizing agent is at least one of triethylamine, triethanolamine, N,N-dimethylethanolamine and diethanolamine; and the amount thereof added is based on a neutralization degree of 95% to 100%.

[0020] Preferably, the addition amount of the alcohol small molecule chain extender and the catalyst respectively accounts for 3% to 6% and 0.05% to 0.1% of the solid matter in the obtained waterborne polyurethane.

[0021] Preferably, the molar ratio of NCO / OH in the waterborne polyurethane prepolymer in step (1) is 1.2 to 1.5; the organic solvent in steps (1) and (3) is acetone, and low-boiling-point acetone can reduce the viscosity of the system and is easy to distill out.

[0022] Preferably, the stirring and dispersing speed in step (2) is 6000 r / min to 7000 r / min, and the emulsification shearing time is 5 min to 10 min.

[0023] Preferably, the stirring reaction in step (3) is carried out at a speed of 4000 r / min to 5000 r / min, and the reaction is first carried out for 20±10 min, and the stirring speed is reduced to 2000±1000 r / min, and the stirring reaction is continued for 30±10 min. Finally, the organic solvent in the emulsion system is removed and the emulsion system is allowed to stand and mature for 24±12 h.

[0024] The waterborne polyurethane prepared by the above method has a solid content of 30% to 35%.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) The aqueous polyurethane nanoemulsion prepared by the present invention has good stability and water resistance, uses water as a dispersion medium, does not contain organic solvents, is green and environmentally friendly, and has a simple process and easy-to-control reaction.

[0027] (2) The present invention uses polyether diol and polycarbonate diol as polyols. Polycarbonate diol has good water resistance and high mechanical strength, and polyether diol has good flexibility. The combination of the two can achieve a balance between softness and hardness.

[0028] (3) The present invention uses anionic and nonionic hydrophilic monomers as internal emulsifiers, so that the prepared aqueous polyurethane emulsion has nanoparticle size and good stability. In particular, the use of nonionic hydrophilic monomers containing polyoxyethylene side chains allows the side chains of polyurethane molecules to have longer polyoxyethylene hydrophilic segments, which not only gives the aqueous polyurethane emulsion good resistance to Ca 2+ 、Na + The good stability of plasma also greatly improves the emulsification capacity of the waterborne polyurethane system and improves its ability to emulsify water-insoluble hydrophobic substances.

[0029] (4) The present invention uses a water-insoluble diamine containing a hydrophobic chain segment as a post-chain extender to post-chain extend the polyurethane prepolymer emulsion. With the help of the emulsification ability of the aqueous polyurethane prepolymer emulsion system prepared by using anionic and nonionic hydrophilic monomers as composite internal emulsifiers, the water-insoluble diamine post-chain extender can enter the interior of the polyurethane prepolymer latex particles and react with the NCO group, and introduce the hydrophobic group into the main chain structure of the polyurethane molecule without substantially changing the particle size and stability of the emulsion (or with a small change), thereby improving the water resistance of the aqueous polyurethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The following are appearance photos of the aqueous polyurethane emulsions prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention.

[0031] Figure 2 The graph is a graph showing the particle size change before and after chain extension of the aqueous polyurethane emulsions prepared in Examples 1-4 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto.

[0033] Example 1

[0034] In a four-necked flask equipped with a stirrer, a thermometer, and a condenser reflux tube, 40.0 g of PH200 with a relative molecular mass of 2000, 40.0 g of polyoxypropylene glycol (PPG) with a relative molecular mass of 2000, 5.0 g of dihydroxymethyl propionic acid, and 6.0 g of Ymer TMN120, heat to 110℃, control the vacuum degree in the reactor to 0.08Mpa after the raw materials are melted, and dehydrate for 1h. Adjust the reaction temperature to 75℃, add 44.0g isophorone diisocyanate and 0.1g dibutyltin dilaurate according to the ratio, and continue to react for 2h. After the reaction is completed, add a mixture of 8.0g 1,4-butanediol and 25.0g acetone dropwise, and continue to react at 75℃ for 2h. Finally, cool to 35℃, add acetone to reduce the viscosity of the prepolymer, and then add 3.5g triethylamine to neutralize and react for 30min to obtain a polyurethane prepolymer with terminal NCO group. After transferring the synthesized polyurethane prepolymer to the dispersion barrel, pour 330.0g of deionized water while increasing the stirring speed to 6000r / min, emulsify and shear for 5min to disperse the prepolymer through phase inversion, then drop 5.0g of 4,4-diaminodicyclohexylmethane and 10.0g of acetone into the mixture for post-chain extension reaction, react for 20min at a stirring speed of 4000r / min, then reduce the stirring speed to 2000r / min and react for 30min before discharging, remove a small amount of acetone in vacuum, let stand and mature for 24h, and then filter through a 200-mesh filter. A water-based polyurethane with a solid content of 30.1% is obtained.

[0035] Example 2

[0036] In a four-necked flask equipped with a stirrer, a thermometer, and a condenser reflux tube, 42.0 g of PH200 with a relative molecular mass of 2000, 40.0 g of polyoxypropylene glycol (PPG) with a relative molecular mass of 2000, 4.7 g of dihydroxymethyl propionic acid, and 5.7 g of Ymer TM N120, heat to 114°C, control the vacuum degree in the reactor to 0.1Mpa after the raw materials are melted, and dehydrate for 1.5h. Adjust the reaction temperature to 80°C, add 40.0g of isophorone diisocyanate and 0.1g of dibutyltin dilaurate according to the ratio, and continue to react for 2h. After the reaction is completed, add a mixture of 7.0g of 1,4-butanediol and 25.0g of acetone dropwise, and continue to react at 80°C for 2h. Finally, cool to 38°C, add acetone to reduce the viscosity of the prepolymer, and then add 3.3g of triethylamine to neutralize and react for 30min to obtain a polyurethane prepolymer with an NCO terminal group. After transferring the synthesized polyurethane prepolymer to the dispersion barrel, pour in 280.0g of deionized water while increasing the stirring speed to 6500r / min, emulsify and shear for 10min to disperse the prepolymer through phase inversion, then drop a mixture of 4.0g 4,4-diaminodicyclohexylmethane and 10.0g acetone to carry out post-chain extension reaction, react for 20min under the stirring speed of 4200r / min, reduce the stirring speed to about 2000r / min, stir for 30min, discharge, remove a small amount of acetone in vacuum, let stand and mature for 24h, and then filter through a 200-mesh filter. A water-based polyurethane with a solid content of 32.8% is obtained.

[0037] Example 3

[0038] In a four-necked flask equipped with a stirrer, a thermometer, and a condenser reflux tube, 40.0 g of PH200 with a relative molecular mass of 2000, 35.0 g of polyoxypropylene glycol (PPG) with a relative molecular mass of 2000, 6.0 g of dihydroxymethyl propionic acid and 6.0 g of Ymer TM N120, heat to 118 ° C, control the vacuum degree in the reactor to 0.09Mpa after the raw materials are melted, and dehydrate for 2h. Adjust the reaction temperature to 82 ° C, add 46.0g of isophorone diisocyanate and 0.1g of dibutyltin dilaurate according to the ratio, and continue to react for 2.5h. After the reaction is completed, add a mixture of 8.0g of 1,4-butanediol and 25.0g of acetone, and continue to react at 82 ° C for 1.5h. Finally, cool to 40 ° C, add acetone to reduce the viscosity of the prepolymer, and then add 4.4g of triethylamine to neutralize and react for 30min to obtain a polyurethane prepolymer with terminal NCO groups. After transferring the synthesized polyurethane prepolymer to the dispersion barrel, pour 280.0g of deionized water while increasing the stirring speed to 7000r / min, emulsify and shear for 15min to disperse the prepolymer through phase inversion, then drop a mixture of 5.9g of 4,4-diaminodicyclohexylmethane and 10.0g of acetone to carry out post-chain extension reaction, react for 20min under the stirring speed of 4500r / min, reduce the stirring speed to about 2000r / min, stir for 30min, discharge, remove a small amount of acetone in vacuum, let stand and mature for 24h, and then filter through a 200-mesh filter. A water-based polyurethane with a solid content of 33.3% is obtained.

[0039] Example 4

[0040] In a four-necked flask equipped with a stirrer, a thermometer, and a condenser reflux tube, 45.0 g of PH200 with a relative molecular mass of 2000, 48.0 g of polyoxypropylene glycol (PPG) with a relative molecular mass of 2000, 7.4 g of dihydroxymethyl propionic acid, and 6.7 g of Ymer TMN120, heat to 120℃, control the vacuum degree in the reactor to 0.1Mpa after the raw materials are melted, and dehydrate for 1.5h. Adjust the reaction temperature to 85℃, add 60.0g isophorone diisocyanate and 0.2g dibutyltin dilaurate according to the ratio, and continue to react for 3h. After the reaction is completed, add a mixture of 11.2g 1,4-butanediol and 25.0g acetone dropwise, and continue to react at 85℃ for 2h. Finally, cool to 42℃, add acetone to reduce the viscosity of the prepolymer, and then add 5.3g triethylamine to neutralize and react for 30min to obtain a polyurethane prepolymer with terminal NCO group. After transferring the synthesized polyurethane prepolymer to the dispersion barrel, pour 340.0g of deionized water while increasing the stirring speed to 7000r / min, emulsify and shear for 15min to disperse the prepolymer through phase inversion, then drop 7.4g of 4,4-diaminodicyclohexylmethane and 10.0g of acetone into the mixture for post-chain extension reaction, react for 20min at a stirring speed of 5000r / min, reduce the stirring speed to about 2000r / min, stir for 30min, discharge, remove a small amount of acetone in vacuum, let stand and mature for 24h, and then filter through a 200-mesh filter. A water-based polyurethane with a solid content of 34.3% is obtained.

[0041] Comparative Example 1: No nonionic hydrophilic chain extender was added

[0042] In a four-necked flask equipped with a stirrer, a thermometer, and a condenser reflux tube, add 45.0g of PH200 with a relative molecular mass of 2000, 48.0g of polyoxypropylene glycol (PPG) with a relative molecular mass of 2000, and 8.5g of dimethylol propionic acid, and heat to 120°C. After the raw materials are melted, control the vacuum degree in the reactor to 0.1Mpa and dehydrate for 1.5h. Adjust the reaction temperature to 85°C, add 60.0g of isophorone diisocyanate and 0.2g of dibutyltin dilaurate according to the ratio, and continue to react for 3h. After the reaction is completed, add a mixture of 11.2g of 1,4-butanediol and 25.0g of acetone dropwise, and continue to react at 85°C for 2h. Finally, cool to 42°C, add acetone to reduce the viscosity of the prepolymer, and then add 6.3g of triethylamine to neutralize and react for 30min to obtain a polyurethane prepolymer with an NCO terminal. After transferring the synthesized polyurethane prepolymer to the dispersion barrel, pour 340.0g of deionized water while increasing the stirring speed to 7000r / min, emulsify and shear for 15min to disperse the prepolymer through phase inversion, then drop 7.4g of 4,4-diaminodicyclohexylmethane and 10.0g of acetone to carry out post-chain extension reaction, react for 20min under the stirring speed of 5000r / min, reduce the stirring speed to about 2000r / min, stir for 30min, discharge, remove a small amount of acetone in vacuum, let stand and mature for 24h, and then filter through a 200-mesh filter. A water-based polyurethane with a solid content of 33.6% is obtained.

[0043] Comparative Example 2: Adding a water-soluble post-chain extender

[0044] In a four-necked flask equipped with a stirrer, a thermometer, and a condenser reflux tube, 42.0 g of PH200 with a relative molecular mass of 2000, 40.0 g of polyoxypropylene glycol (PPG) with a relative molecular mass of 2000, 4.7 g of dihydroxymethyl propionic acid, and 5.7 g of Ymer TM N120, heat to 114°C, control the vacuum degree in the reactor to 0.1Mpa after the raw materials are melted, and dehydrate for 1.5h. Adjust the reaction temperature to 80°C, add 40.0g of isophorone diisocyanate and 0.1g of dibutyltin dilaurate according to the ratio, and continue to react for 2h. After the reaction is completed, add a mixture of 7.0g of 1,4-butanediol and 25.0g of acetone dropwise, and continue to react at 80°C for 2h. Finally, cool to 38°C, add acetone to reduce the viscosity of the prepolymer, and then add 3.3g of triethylamine to neutralize and react for 30min to obtain a polyurethane prepolymer with an NCO terminal group. After transferring the synthesized polyurethane prepolymer to the dispersion barrel, pour 280.0g of deionized water while increasing the stirring speed to 6500r / min, emulsify and shear for 10min to disperse the prepolymer through phase inversion, then drop 3.3g of isophorone diamine and 10.0g of water for post-chain extension reaction, react for 20min at a stirring speed of 4200r / min, reduce the stirring speed to about 2000r / min, stir for 30min, discharge, remove a small amount of acetone in vacuum, let stand for aging for 24h, and then filter through a 200-mesh filter. A water-based polyurethane with a solid content of 32.8% is obtained.

[0045] Experimental results test and analysis:

[0046] The performance test method of the product obtained in the above embodiment:

[0047] 1. Film water absorption test

[0048] Preparation of adhesive film: Weigh an appropriate amount of the prepared aqueous polyurethane emulsion and spread it evenly on a polytetrafluoroethylene plate, place it horizontally, and dry it naturally at room temperature for 3 days. After the adhesive film is formed, put it in a 50°C oven and dry it to constant weight, and put it in a desiccator for later use.

[0049] Determination of water absorption: Cut the film into 2cm×2cm pieces, weigh them on an analytical balance, record the weight as M0, soak them in deionized water for 24 hours, take them out, dry the surface water with filter paper, weigh them again, record the weight as M1, and calculate the water absorption of the latex film according to the following formula:

[0050] Water absorption rate W / % = (M1-M0) / M0×100%

[0051] 2. Emulsion particle size test:

[0052] The particle size and its distribution were determined by dynamic light scattering (DLS, Malvern, ZS-Nano-S) at 25°C. The prepared aqueous polyurethane emulsion was diluted to 0.1wt% with deionized water, and the average particle size, particle size distribution and Zeta potential of the diluted aqueous polyurethane were measured. The results are the average of three tests.

[0053] 3. Ionic stability:

[0054] In a 10ml test tube with a scale, add 5ml of the prepared aqueous polyurethane emulsion with a dropper, and then slowly add 1ml of 1% NaCl solution or 1ml of 0.1% CaCl2 solution. After shaking thoroughly, place on a test tube rack. After 24 hours, observe whether the emulsion breaks, precipitates, flocculates, etc.

[0055] 4. Storage stability

[0056] The storage stability was simulated by centrifuge accelerated sedimentation test. The same mass of prepared waterborne polyurethane emulsion was placed in a centrifuge tube, and the tube was placed symmetrically in a centrifuge at a speed of 3000r / min for 15 minutes. Observe whether the emulsion is stratified. If not, it can be considered to have a storage stability period of 6 months.

[0057] Table 1 Particle size changes of waterborne polyurethane emulsion before and after chain extension

[0058]

[0059] It can be seen from Table 1 that in the waterborne polyurethane prepared by using the water-insoluble hydrophobic post-chain extender, the particle size is smaller after the addition of the non-ionic hydrophilic monomer and the chain extension. This shows that when the anionic-non-ionic hydrophilic monomer is used as the hydrophilic chain extender, the waterborne polyurethane can be endowed with a stronger self-emulsification and dispersion ability, which is conducive to the water-insoluble hydrophobic diamine chain extender entering the waterborne polyurethane prepolymer emulsion particles to react, thereby obtaining a waterborne polyurethane with a smaller particle size.

[0060] Table 2 Appearance, stability and water absorption of waterborne polyurethane emulsion

[0061]

[0062]

[0063] It can be seen from Table 2 that the waterborne polyurethane emulsions prepared by adding nonionic hydrophilic monomers have high transparency and good Ca resistance. 2+ 、Na +Stability. Compared with the waterborne polyurethane prepared by using water-soluble hydrophobic post-chain extender, the waterborne polyurethane prepared by using water-insoluble hydrophobic post-chain extender has a lower water absorption rate, which indicates that the water-insoluble hydrophobic post-chain extender can introduce stronger hydrophobic chain segments during the post-chain extension reaction and can more effectively reduce the penetration of water molecules.

[0064] Table 3 Stress (tensile strength) and strain (elongation at break) of waterborne polyurethane before and after soaking in water

[0065]

[0066] As can be seen from Table 3, the stress of the waterborne polyurethane prepared by using the non-water-soluble hydrophobic post-chain extender did not change much after being soaked in water for 24 hours, indicating that the use of the non-water-soluble hydrophobic post-chain extender can not only reduce the penetration of water molecules into the polyurethane, but also effectively improve the hydrolysis resistance stability of the waterborne polyurethane. However, when the non-ionic hydrophilic monomer is not added, the particle size of the prepared waterborne polyurethane emulsion is large and the stability is poor due to the uneven post-chain extension reaction process, resulting in poor hydrolysis resistance stability.

[0067] From the above test results, the aqueous polyurethane emulsion prepared by the present invention has excellent electrolyte resistance stability, an average particle size of 30 to 40 nm, not only low water absorption but also excellent hydrolysis resistance stability, non-toxicity, safety and environmental protection, simple process, stable and easy operation, and convenient product transportation and use.

[0068] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing an aqueous polyurethane with good water resistance, characterized in that: The method comprises the following preparation steps: (1) vacuum dehydrating a polyol, an anionic hydrophilic chain extender, and a nonionic hydrophilic chain extender containing a polyoxyethylene side chain, and then adding a polyisocyanate to carry out a polymerization reaction to obtain a polyurethane prepolymer; (2) dispersing the polyurethane prepolymer into water under high-speed stirring to obtain a prepolymer emulsion; (3) adding a mixed solution of a water-insoluble diamine post-chain extender containing hydrophobic chain segments and an organic solvent to the prepolymer emulsion obtained in step (2), stirring and reacting, and obtaining a water-based polyurethane with good water resistance.

2. The preparation method according to claim 1, characterized in that: The water-insoluble diamine post-chain extender containing hydrophobic chain segments in step (3) includes a mixture of one or more of 3,5-diethyltoluenediamine, 4,4-diaminodicyclohexylmethane, 4,4-diaminodiphenylmethane, N,N-di-sec-pentylcyclohexanediamine, 2,4,4-trimethylhexamethylenediamine, 2-aminobenzamide toluenediamine, and 3,5-dimethylthiotoluenediamine.

3. The preparation method according to claim 2, characterized in that: The anionic hydrophilic chain extender in step (1) is a mixture of one or more of a carboxylic acid chain extender and a sulfonate chain extender; the nonionic hydrophilic chain extender is a diol containing a polyoxyethylene side chain; and the polyol is a polyether polyol and a polycarbonate polyol with a molecular weight of 1000 to 2000.

4. The preparation method according to claim 3, characterized in that: The anionic hydrophilic chain extender is dimethylol propionic acid; the polyether polyol is a mixture of one or more of polytetramethylene glycol and polyoxypropylene glycol; the polycarbonate polyol is a mixture of one or more of aliphatic polycarbonate polyol and aromatic polycarbonate polyol; The polyisocyanate is at least one of hexamethylene diisocyanate, isophorone diisocyanate and dicyclohexylmethane diisocyanate.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The polyol, polyisocyanate, anionic hydrophilic chain extender, nonionic hydrophilic chain extender and post-chain extender in step (1) are added in amounts accounting for 50% to 60%, 25% to 32%, 2.5% to 5%, 2.5% to 5% and 2% to 4% of the solid matter of the obtained waterborne polyurethane, respectively.

6. The preparation method according to claim 5, characterized in that: In the polymerization reaction of step (1), a catalyst is added, and the reaction is carried out at a temperature of 75 to 85° C. for 2 to 3 hours. Then, a mixture of an alcohol small molecule chain extender and an organic solvent is added dropwise, and the reaction is continued for 1 to 2 hours. Finally, the temperature is lowered to 35 to 50° C., an organic solvent is added to reduce the viscosity of the prepolymer, and then a neutralizer is added to react for 0.5±0.1 hour to obtain a polyurethane prepolymer.

7. The preparation method according to claim 6, characterized in that: The alcohol small molecule chain extender is at least one of ethylene glycol, 1,4-butanediol, hexanediol, and diethylene glycol; the catalyst is at least one of dibutyltin dilaurate and stannous octoate; The neutralizing agent is at least one of triethylamine, triethanolamine, N,N-dimethylethanolamine and diethanolamine; The added amounts of the alcohol small molecule chain extender and the catalyst respectively account for 3% to 6% and 0.05% to 0.1% of the solid matter in the obtained waterborne polyurethane.

8. The preparation method according to claim 7, characterized in that: The molar ratio of NCO / OH in the waterborne polyurethane prepolymer in step (1) is 1.2 to 1.5; the vacuum dehydration conditions are: heating to 110 to 120° C., controlling the vacuum degree in the reactor to 0.08 MPa to 1 MPa after the raw materials are melted, and dehydrating for 1 to 2 hours; the organic solvent in steps (1) and (3) is acetone; The speed of the high-speed stirring in step (2) is 6000 r / min to 7000 r / min, and the stirring time is 5 min to 10 min; The stirring reaction in step (3) is carried out at a speed of 4000 r / min to 5000 r / min, and the reaction is first carried out for 20±10 min, and then the stirring speed is reduced to 2000±1000 r / min, and the stirring reaction is continued for 30±10 min; finally, the organic solvent is removed and the mixture is allowed to stand and mature for 24±12 h.

9. Aqueous polyurethane prepared by the method according to any one of claims 1 to 8.

10. The waterborne polyurethane according to claim 9, characterized in that: The solid content of the waterborne polyurethane is 30% to 35%.

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